The present invention relates generally to inkjet printing mechanisms, and more particularly to an ink solvent application system that applies an inkjet ink solvent using a wiper system to clean inkjet printheads.
Inkjet printing mechanisms use cartridges, often called xe2x80x9cpens,xe2x80x9d which eject drops of liquid colorant, referred to generally herein as xe2x80x9cink,xe2x80x9d onto a page. Each pen has a printhead formed with very small nozzles through which the ink drops are fired. To print an image, the printhead is propelled back and forth across the page, ejecting drops of ink in a desired pattern as it moves. The particular ink ejection mechanism within the printhead may take on a variety of different forms known to those skilled in the art, such as those using piezo-electric or thermal printhead technology. For instance, two earlier thermal ink ejection mechanisms are shown in U.S. Pat. Nos. 5,278,584 and 4,683,481. In a thermal system, a barrier layer containing ink channels and vaporization chambers is located between a nozzle orifice plate and a substrate layer. This substrate layer typically contains linear arrays of heater elements, such as resistors, which are energized to heat ink within the vaporization chambers. Upon heating, an ink droplet is ejected from a nozzle associated with the energized resistor. By selectively energizing the resistors as the printhead moves across the page, the ink is expelled in a pattern on the print media to form a desired image (e.g., picture, chart or text).
To clean and protect the printhead, typically a xe2x80x9cservice stationxe2x80x9d mechanism is supported by the printer chassis so the printhead can be moved over the station for maintenance. For storage, or during non-printing periods, the service stations usually include a capping system which substantially seals the printhead nozzles from contaminants and drying. Some caps are also designed to facilitate priming, such as by being connected to a pumping unit that draws a vacuum on the printhead. During operation, clogs in the printhead are periodically cleared by firing a number of drops of ink through each of the nozzles in a process known as xe2x80x9cspitting,xe2x80x9d with the waste ink being collected in a xe2x80x9cspittoonxe2x80x9d reservoir portion of the service station. After spitting, uncapping, or occasionally during printing, most service stations have an elastomeric wiper that wipes the printhead surface to remove ink residue, as well as any paper dust or other debris that has collected on the printhead. The wiping action is usually achieved through relative motion of the printhead and wiper, for instance by moving the printhead across the wiper, by moving the wiper across the printhead, or by moving both the printhead and the wiper.
To improve the clarity and contrast of the printed image, recent research has focused on improving the ink itself. To provide quicker, more waterfast printing with darker blacks and more vivid colors, pigment-based inks have been developed. These pigment-based inks have a higher solid content than the earlier dye-based inks, which results in a higher optical density for the new inks. Both types of ink dry quickly, which allows inkjet printing mechanisms to form high quality images on readily available and economical plain paper, as well as on recently developed specialty coated papers, transparencies, fabric and other media.
As the inkjet industry investigates new printhead designs, the tendency is toward using permanent or semi-permanent printheads in what is known in the industry as an xe2x80x9coff-axisxe2x80x9d printer. In an off-axis system, the printheads carry only a small ink supply across the printzone, with this supply being replenished through tubing that delivers ink from an xe2x80x9coff-axisxe2x80x9d stationary reservoir placed at a remote stationary location within the printer. Since these permanent or semi-permanent printheads carry only a small ink supply, they may be physically more narrow than their predecessors, the replaceable cartridges. Narrower printheads lead to a narrower printing mechanism, which has a smaller xe2x80x9cfootprint,xe2x80x9d so less desktop space is needed to house the printing mechanism during use. Narrower printheads are usually smaller and lighter, so smaller carriages, bearings, and drive motors may be used, leading to a more economical printing unit for consumers.
There are a variety of advantages associated with these off-axis printing systems, but the permanent or semi-permanent nature of the printheads requires special considerations for servicing, particularly when wiping ink residue from the printheads. Any abrasive wiping contact with the printheads could induce premature printhead failure, or degrade the print quality of the printed images. Thus, it would be desirable to have a printhead wiping system which cleans the printheads without any appreciable wear to promote an extended printhead lifespan.
According to one aspect of the present invention, a wiping system for cleaning an inkjet printhead in an inkjet printing mechanism. The wiping system includes a wiper, and a platform that supports the wiper for rotational movement and for translational movement between an application position and a wiping position for cleaning ink residue from the printhead. The wiping system has an ink solvent applicator impregnated with an ink solvent, with the applicator being located for contact with the wiper when the wiper is moved to the application position. The platform moves the wiper away from the applicator with a combination of both rotational movement and translational movement to retain the ink solvent on the wiper.
According to a further aspect of the present invention, an inkjet printing mechanism may be provided with a wiping system as described above.
According to another aspect of the present invention, a method of cleaning ink residue from an inkjet printhead in an inkjet printing mechanism is provided. This method includes a step of applying an ink solvent to a wiper by: (a) contacting the wiper with an applicator of a porous material impregnated with the ink solvent, (b) extracting the ink solvent from the applicator as a meniscus of solvent clinging to both the wiper and the applicator, and (c) lifting the wiper away from the applicator after allowing the meniscus to substantially reach equilibrium to retain the ink solvent on the wiper. In a wiping step, the ink residue is wiped from the printhead and a portion of the ink residue is dissolved in the ink solvent which was retained on the wiper.
According to a further aspect of the present invention, another method of cleaning ink residue from an inkjet printhead in an inkjet printing mechanism. This method includes a step of applying an ink solvent to a wiper by: (a) contacting the wiper with an applicator of a porous material impregnated with the ink solvent, (b) extracting the ink solvent from the applicator through capillary forces and into a capillary region defined between the applicator and the wiper, and (c) moving the wiper away from the applicator with both rotational movement and translational movement to retain the ink solvent on the wiper. In a wiping step, the ink residue is wiped from the printhead and a portion of the ink residue is dissolved in the ink solvent which was retained on the wiper.
According to still a further aspect of the present invention, an additional method of cleaning ink residue from an inkjet printhead in an inkjet printing mechanism is provided. This method includes the step of applying an ink solvent to a wiper by: (a) dragging the wiper in a first direction across an applicator of a porous material impregnated with the ink solvent to extract the ink solvent from the applicator trough capillary forces to form a meniscus of solvent between the wiper and the applicator, (b) pausing motion of the wiper after said dragging step to allow the meniscus to substantially reach equilibrium, and (c) removing the wiper from the applicator to retain the ink solvent on the wiper by simultaneously moving the wiper away from the applicator while also moving the wiper in a direction opposite said first direction. In a wiping step, the ink residue is wiped from the printhead and a portion of the ink residue is dissolved in the ink solvent which was retained on the wiper.
An overall goal of the present invention is to provide an inkjet printing mechanism which prints sharp vivid images over the life of the printhead and the printing mechanism, particularly when using fast drying pigment or dye-based inks, and preferably when dispensed from an off-axis system.
Another goal of the present invention is to provide an ink solvent application system for cleaning printheads in an inkjet printing mechanism to provide consumers with a reliable, economical inkjet printing unit.